3.Deadlock Prevention
>Mutual Exclusion- Not required for sharable resources;
must hold for nonshareable resources.
>Hold and Wait- must guarantee that whenever a process request a resource, it does not hold any other resources.
-require process to request and be allocated all its resource before it begins execution, or allow process to request a resource only when the process has none.
- low resource utilization: starvation possible.

>No Preemption
if a process that is holding some resoureces requests
another resource that cannot be immediately allocated to it,
then all resources currently being held are released
- preemted resources are added to the list of resources for which the process is waiting.
process will be restarted only when it can regain its old resources, as well as the new
ones that it is requesting
>Circular wait- impose a total ordering of all resource types, and require that each process requests resources in an incresing order of enumeration..,